Prior Art
Heretofore known are confidential sheets adapted to bear concealed information to assure secrecy and continuous strips for forming such sheets. For example, envelope sheets or strips and envelopes or the like prepared therefrom are disclosed in Examined Japanese Patent Publication SHO 51-30830, Examined Japanese Utility Model Publication SHO 59-41113, Unexamined Japanese Utility Model Publication SHO 60-142970, etc.
With reference to FIG. 24, such an envelope 10d comprises a first piece of paper 1d having an address bearing area 2d on its front surface, a second piece of paper 1e having an information bearing area 3d on its front surface and a third piece of paper 1f which are integral with one another with folds 4d, 4e formed therebetween. Adhesive coatings 5d, 6d are formed at the outer peripheral portion of the combination of the second and third paper pieces 1e, 1f on the front surface and at the outer peripheral portions of the first and second paper pieces 1d, 1e on the rear surface. The three pieces 1d, 1e, 1f as folded in three are joined together with the adhesive coatings 5d, 6d.